Facebook is expanding its Instagram photo-sharing app to include 15-second user-captured video -- a development that stands to give media and entertainment companies a powerful new marketing tool on the world's biggest social-media service.

"We need to do to video what we did to photos," Instagram CEO and co-founder Kevin Systrom said at a press conference Thursday.

Instagram set the 15-second limit because that's not too short to "constrain your creativity" but not too long to require users to wait for video to upload from their mobile devices, he said.

The move is aimed a one-upping Facebook's social-media rival, Twitter. Last fall Twitter acquired Vine, whose app is designed for sharing six-second video clips on social sites. According to Twitter, Vine has 13 million users.

According to Systrom, 130 million people use Instagram every month. Facebook acquired Instagram in April 2012 for $1 billion. Facebook itself had 1.11 billion monthly active users as of March 2013.

To date, Instagram users have shared 16 billion images, according to Systrom: "That's a lot of pictures of coffee," he said, eliciting chuckles from the audience.

Video on Instagram will provide 13 different video-effect filters, such as "moon" and "vesper," similar to the photo filters in the app. "It wouldn't be Instagram without being beautiful," Systrom said.

Another video feature, dubbed "Cinema," provides stabilization features to eliminate the shakiness in video recorded on a handheld device. The video on Instagram feature is available on both Apple iOS and Android devices from day one, Systrom said.

Instagram had originally considered creating an app for sharing both video and photos, but two years ago the capabilities of smartphones and wireless networks weren't good enough to make video-sharing viable, Systrom said. Instagram now has 35 employees, operating as a unit within Facebook.

The business model for Instagram has never been clear. The app is free to use, and does not carry any advertising.